Good advice.  I go to every class available at my dojo.  I am 85 and took Japanese Ju jitsu in the mid 70's, then restarted 9 months ago as a newbie.  I roll with everyone, except one 210 lb guy who is just too much for my 125 lb body.  I regularly get tapped by everyone, including the 11 y.o. kids.  I get back into it because it is fun and I need the high intensity exercise.  I do need to experiment more rather than just defending.

“Start from the guard”

This is extremely important, because the guard-fighting skills form the base of all groundfighting skills.  From the guard, your opponent can drive his weight into you to control you, but you can use your legs to control him.  If you can win that battle, then you can influence the tide of battle of the whole match in your favor.
I would add to that, “ditch the kneeling position”.  That is because the kneeling position gives you a way to avoid working on your guard. As was stated, “view a loss in class as an opportunity to learn”.  Another way of saying that is, “Leave your ego at the door.”  In class, do not worry about winning or losing.  Even if it means losing to the lowest ranking white belt.  Combine that with working on your guard.  Work on your guard without worrying if you get passed, or even tapped.

I think understanding that you get nowhere fast regarding BJJ is also a good way to keep showing up and keep improving.

"Be there mentally" - that is so true. After thaiboxing. My head is floating while doing drills. I am trying to figure out a way to do it with more mental presence.

You see the ballet dancers  warm up on the barre, thats fundamentals training, the do it all the time before the real perfomance .

Thank you 👍👍

Develop solid fundamentals.